A variety of front suspension systems have been employed on snowmobiles over the years. In the early 1980s, the assignee of the present invention introduced to the snowmobiling industry an independent front suspension system utilizing a trailing arm—an elongated arm having its front end rigidly connected to the steering spindle and its rear-end pivotally connected to the chassis. See Canadian Patent No. 1,227,823, and also U.S. Pat. Nos. 6,328,124 and 6,343,666. Front suspension systems employing trailing arms have been widely accepted in the snowmobile industry. When a snowmobile ski encounters an object during operation, the suspension system is designed to permit the ski to travel over the object while providing a relatively smooth, controlled ride to the driver. Some of the force of the perturbance is transmitted by the trailing arm to the chassis, and this in turn produces a yaw moment. Also, as illustrated in FIGS. 1 and 2 of the drawing, the necessary positioning of the trailing arm takes up space and increases the difficulty of appropriately and functionally designing that area of the vehicle.
Moreover, the stiffness of the front suspension of the snowmobile is important both to the rider's comfort and the ability to control the snowmobile. On the one hand, the suspension should be sufficiently “soft” as to provide a smooth ride over fairly level ground. On the other hand, the suspension should be sufficiently stiff so that the snowmobile suspension does not “bottom out” when the snowmobile is operated in rough terrain. Shock absorbers are commonly used for this purpose, and have been commonly mounted in snowmobiles with trailing arm suspensions such that as the suspension is compressed, the compressive axis of the shock absorber becomes less aligned with the generally vertical direction of ski displacement with respect to the chassis, and this leads to the suspension becoming softer as the front suspension is compressed, in turn leading to bottoming-out problems. That is, the motion ratio of shock absorber movement to vertical ski movement may be reduced as the suspension is compressed, leading to a diminished ski rate.
It may be appreciated that suspension systems for snowmobiles are in fact quite sophisticated, technically. Not only must one consider the problems raised above in connection with trailing arm suspensions, but also problems involving caster angle and ease of steering and control, problems involving the tendency of a snowmobile to “dive” when braked hard or when encountering obstacles, and problems involving the expected increase in camber angle (and the resulting tendency of the skis to “scrub” or drift sideways) when the chassis of the snowmobile rolls during sharp turns.
The applicants have now found that further improvements in front suspension systems can be made to avoid trailing arms while maintaining high performance advantages for the rider.